To determine if unilateral pedicle screw fixation is comparable to bilateral fixation in one-or two-segment lumbar spinal fusion.

Eighty-eight patients with spinal stenosis or spondylolisthesis were assigned to either unilateral or bilateral pedicle screw instrumentation groups. Demographic variables, preoperative diagnosis, number of fusion segments, and kinds of instrumentation used were similar between the two treatment groups.

There were no significant differences between the two groups in terms of blood loss, clinical results, time at which fusion was complete, fusion rate, and complication rate. There were significant differences between the two groups in terms of duration of operating time, duration of hospital stay, medical expenses. The number of fusion segments or kinds of instrumentation did not affect the fusion rate, time at which fusion was complete, or clinical outcomes. Metal failure rate of unilateral fixation was higher in patients with spondylolytic spondylolisthesis than in patients with spinal stenosis.

Unilateral pedicle screw fixation was as effective as bilateral pedicle screw fixation in lumbar spinal fusion independent of the number of fusion segments (one or two segments) or pedicle screw systems. Unilateral pedicle screw fixation is not recommended for spondylolytic spondylolisthesis patients who were treated with Gill' s decompression.